Examples of the present invention relate to a system measuring biological information.
A pulse photometer is known as an example of an apparatus constituting such a biological information measurement system. A pulse photometer is an apparatus for calculating the concentration of a light absorbing substance in blood of a subject. Specifically, light having a plurality of wavelengths illuminates the biological tissue of the subject. The plurality of wavelengths are determined so that the ratio of the absorption coefficients of blood differs depending on the concentration of the light absorbing substance in blood. The amount of light having each wavelength transmitted through or reflected by the biological tissue is detected. The light amount of each wavelength depends on the pulsation of the blood of the subject. Accordingly, the time-dependent change of the light amount of each wavelength caused by the pulsation is obtained as a pulse wave signal. The amplitude of the pulse signal of each wavelength corresponds to the attenuation change amount of the waveform. The concentration of the light absorbing substance in blood is calculated based on the ratio of the attenuation change amount of each waveform (see JP-B-53-026437, for example).
Arterial blood oxygen saturation is known as the concentration of a light absorbing substance in blood. Arterial blood oxygen saturation is the ratio of oxyhemoglobin to the amount of hemoglobin capable of carrying oxygen. That is, oxyhemoglobin is an example of a light absorbing substance in blood. Another example of a light absorbing substance in blood is a dye as an indicator to be administered to a blood flow to measure the transit time of the biological tissue.